XOTES
July, 1963 guanidine.2 A. possible method for the formation of biguanide may be postulated to 0ccu.r by equation 1.
NH&14NH
+ ?;HZC(NH)KHa --+KH,C14(NH)KHC(SH)NHZ (1)
Certainly, alternate possibilities for the formation of biguanide-CI4 could be written. Degradation studies of cyanoguanidine, melamine, acetamidine, and biguanide, which would indicate the percentage of the carbon-14 labeling a t each carbon position, mere not performed, so we are unable to indicate specifically the degree of labeling of the carbon-14 positions in the product molecules. The neutron irradiation of crystalline guanidine hydrochloride does not cause incorporation of carbon-14 into the "simple" molecules. We would suggest that the incorporation of the recoil carbon-14 atom into the more complex chemical species occurs oia replacement reactions of the recoil carbon-14 atom with the guanidine molecule of the matrix to produce the cyanamide radical. This radical then further reacts with other species present in the matrix to produce the final products observed. The study of the radiocarbon-labeled compounds produced by the neutron irradiation of cyanoguanidine2 and the results of this study appear to occur by the same process, i.e., the intermediate formation of the radiocarbon-labeled cyanamide radical. Certainly the final products observed in solution in both of these studies are readily explained in terms of similar reactions. Acknowledgments.--The initial stages of this research were supported in part by a grant from the Petroleum Research Fund administered by the American Chemical Society. Grateful acknowledgment is hereby made to the donors of said fund. PREPARATION AND STUDY 03' ORDERING I N A(B1o.33Nb0.6~)03 PEROVSKITE-TYPE COMPOUNDS BY FRANCIS GALASSO AND JANE PYLE rnzted Azrcraft Corporatzon, Research Laboratorzes, East Hartford, Connectacul Recezued Janunrg 16, 1963
The perovskite structure adopted by many ABQ3type compounds can be described by a cubic unit cell with a large X ion at the center, smaller B ions situated a t the corners, and oxygen ions on the edges. When ions of more than one element are present in the B position, the possibility of these ions being ordered exists. A study of Ba(B'o.3bo5)03-type compounds demonstrated that size and charge difference of the B position ions had an important, effect on their ordering.' In a more recent investigation of A(B'o.33Tao.67)03-type compounds, where A is a barium or strontium ion and B' is a smaller divalent ion, these results not only were substantiated but it also was found that the degree of longrange ordering in the B position ions decreased as the difference in the size of these ions became smaller.2 In order t o test the generality of these results for other perovskite-type compounds with two different ions in the B position, a study of ordering was undertaken in a n (1) F. Galasso and W. Darby, J . Phya. Chsm., 60, 131 (1962). (2) F. Galasso and J. Pyla, Inoru. Chcm,, P, 482 (1963).
1561
_1
i
w
u
t 3 E
1. 4
z
0 0 4 X
w
r
U
0
LT
0 i
W
u
c2 a
0 3 0 U
oa 0
06
07 IONIC
Fig. 1.-Ionic
os RADII
69 OF
I O
I I
12
B' I O N , A H R E N S V A L U E S .
radii of B' ions us. cell size for A(B'0.33B''o.6,)013type compounds.
analogous series produced by substituting niobium for tantalum in the A( B'0.33Tao.6,)03 compounds. The results of this study are presented in this note. Experimental Most of the compounds were mixed according to the equation
ACOs
+ '/3B'O + '/&b205
A(B'o.aNbo.e7)03
+ COz
--+
where A is a strontium or barium ion and B' is a divalent metal ion. The mixtures were heated a t 1000" for 10 hr., reground, and reheated a t 1400'' for 4 hr. Powder X-ray photographs then were taken of the compounds using a Philips 57.3-mm. radiiis camera with Cu Ka! radiation and settings of 40 kv., 30 ma. for 4 hr. For compounds in which B' was cadmium or lead, the X-ray photographs urged for indexing were taken using the powders prepared a t 1000" because the perovskite phafie was found to decompose a t higher temperatures and either a phase became predominant.8 BasNbrOla or SrsSb4OI6 When the B' ion was iron, strontium or barium oxide was used in place of the carbonates and the compounds were mixed in proportions dictated by the equation
A0
+ 'IsFe + '/J7ez03 + II3Nb2O5 A( Ferro33XbV0.6i) 0
3
These samples were made into pellets, sealed under vacuum in silica capsules, and heated for approximately 10 hr. a t a maximum temperature of 11100° because they melted through the silica a t higher temperatures The procedure of heating the compounds to approximately 1400", when possible, before taking Xray powder diffraction photographs a t room temperature was adopted from a similar study of A(B'o.3aTao.o7)Oa-type compounds for the following reason.2 When the samples in that study were prepared a t 1000" or lower, their X-ray pattern showed ordering lines which were often weak and diffuse and sometimes not even visible. However, if the samples could be heated several hundred degrees higher, presumably the size of the ordering domain8 was increased which in turn caused the reflections due to ordering to become much sharper. Since similar behavior was oherved (3) F,Galasso and L. Kate, Acta Cryet,, 14, 647 (1961).
NOTES
1562
Vol. 67
for many of the compounds in this study, it could not be positively concluded that compounds containing iron, cadmium, or lead as the B’ ion, -which could not be heated above the 1000-1100” temperature range, were not ordered even though no ordering lines were visible in their X-ray patterns. However, for the purpose of this study compounds containing cadmium, lead, or iron were indexed on the basis of an -4 -4.cubic perovskite unit cell with the exception of Sr(Feo33Nb0 6i)Odwhich was indexed on a small tetragonal unit cell All other compounds, except Ba(Zno 33Nb06 7 ) 0 3 and Ba(Sio 33?jb6 ~ ) 0 3 ,gave X-ray patterns similar to that of the ordered perovskite Ba(Sr0 z3Tafl6?)Osand, therefore, were indexed on the basis of hexagonal unit cells.4
(hIg0.a,Sb~.m)03 and Ba(Zn,.&bo.~,)0~,would not have an ordered structure because of the small differences in the ionic radii of their B ions. It was surprising to find that Ba(h1g0.&\;0.67)0~,which has a much smaller difference in the radii of its B ions than the zinc compound, adopts the ordered structure. Figure 1 shows, however, that the magnesium ion appears to be much larger in these compounds than Ahrens’ value5 for the radius indicates. If this is the case, the difference in size between the magnesium and niobium ionswouldbe somewhat greater than is indicated in Table I, but still not Discussion and Results large enough to be the only cause of ordering in this In a previous study it was observed that any of the compound. A(B’0.33Ta~.~,)0~ compounds which could be heated to Since Sr(T\lio.3~Pl‘bo.6~)03 and Sr(Zn0.33?;b~.67)03 have approximately 1400’ showed evidence of having the the ordered structure while the analogous compounds Ba(Sr0.33Ta0.67)O~ordered perovskite-type structure, with barium in the A position do not, it appears that and also that the degree of ordering in the B position the small size of the A ion also may be a factor contribdecreased as the size of the B ions decreased.2 If the to ordering. It must be noted, however, that uting compounds which could not be heated higher than 1 1 0 0 O the size and charge difference of the B ions appear to be are not considered, the results of this study on analogous the most important causes of their ordering in these niobium compounds with the general formula A(B’0.33compounds, and it is only when their effect is minimized Pl’b0.~)03are quite similar (see Table I). The most that other factors become most influential in producing interesting difference found between the A(B’0.33an ordered arrangement of B ions. Kbo.~)Oaand A ( B ’ O . ~ ~ T ~ compounds ~ . ~ , ) O ~ lies in the fact that the B ions were ordered in Ba(!4no.33Ta~.67)03 and Ba(Ni0.33Ta0.6,)03, but no evidence of ordering was found IKTENSITY OF THE 9 kK.B h S D BXD in the Ba(Zn0.33Kb0.~)0~ and Ba(Xo.&b~.6,)03 X-ray MOLECULAR ASSOCIATION IS TANADIUM patterns even though the size and charge of the tanTETRACHLORIDE’ talum and niobium ions are similar. For the series of BY EUGENE L. GRUBB,F. A. BLAKKENSHIP, AND Ba(B’0.3~Eb~.67)0. compounds listed in Table I, it seemed R. LINNBELFORD~ most reasonable that Ba(B’o.33Nbo.67)03, along with BaNoyes Chemical Laboralory, University of Illanois, Urbana, Ilknoas
TABLE I
Received February 6. 1965
STRUCTURE DATAFOR A(B’0.33Kbfl.67)03 COMPOUNDS
Celld Compound
size,
A.
Difference in Ionio ionic radii radii of B of B‘ ion, position ions, A.
:I
Unit cell
Ba(hIg0.83Nb0.67)03Ea = 5 77 0.67 0.02 Hexagonal c = 7.08 .69 .OO Cubic Ba(n’i0 &bo.67)03b a = 4.074 a = 4.094 .74 .05 Cubio Ba(Zn0 33Kb0.67)030 .74 .05 Cubic Ba(Fe0 33Nbo 6?)03 a = 4.085 .97 .28 Cubic Ba(Cdo 33Sb0 6 7 ) 0 3 a = 4.168 .99 .30 Hexagonal Ba(Cao.&bo 6 7 ) 0 3 a = 5.92 c = 7.25 Ba(Pbo.&bO 87)Oz a = 4.26 1.20 .51 Cubic Sr(h!Igo.33Nb06 7 ) 0 3 a = 5.66 0.67 .02 Hexagonal c = 6.98 Sr(Ni0.33Kb067)03 a = 5.64 .69 .OO Hexagonal c = 6.90 S I ( Z ~ ~,i)O3” . ~ ~ aN =~ 5.66 ~ .71 .05 Hexagonal c=695 Sr(Fe033Sb06i)Os a = 3.997 .74 .05 Tetragonal c = 4 018 Sr(Cd0 33Nb0 a = 4 089 .94 .28 Cubic Sr(Cao 33NbO 6 7 ) 0 3 a = 5 76 .99 .30 Hexagonal c = 7.16 a Ahrens ionic radii values used.6 Reported by R. Roy, indexed on cubic cell.n Reported by F. Galasso, L. Katz, and %. Ward, indexed on cubic cell.? EstimFted error of f0.001 A. for values given to three places, f0.005 A. for values given to two places. (4) F. Galasso, J. R. Barrante, and L. Katz, J. Am. Chem. Soe., 83,2830 (1061). (5) L. €I. Ahrens, “Use of Ionization Potentials: 1, Ionic Radii of the Elements,” Geocham. et Cosmochzm, Acta, 8 , 155 (1962). (6) R.Roy, J . A m . Ceramzc Soc., 57, 581 (1954). I?) F. Galasso, L. Katz, and R . Ward, J . A m . Chem. Soe., 81, 820 (1959).
The absolute intensity of B ligand field transition of a simple molecule such as VC1, provides a very useful test for molecular calculations. Since the only previous experimental studies3+ of the VC14 ligand-field bands (-9 kK.) did not provide a reliable oscillator strength we undertook to properly measure it over a small temperature and pressure range. The possibility that strong intermolecular forces are important in VC14 in condensed phases has been suggested. The question is crucial in interpretation of optical and magnetic properties. To test this, we also studied band shape and intensity of the 9 kK. band of VC1, in condensed phases. In so doing, we obtained some vapor pressure data which substantiate VCI, as being a “normal” (Le., unassociated) liquid a t and above room temperature. Experimental Four series of measurements were carried out. Series 1.-An apparatus explained and diagrammed in ref. 6 was used. The arrangement allowed the temperature and pressure of the vapor sample t o be varied independently. The highly purified sample was sealed into an all-glass apparatus having a glass-sickle null pressure indicator. Since the 9 kK. band shape varies very little over the 25-70’ range, the integrated intensity is proportional to peak intensity to &37’,,44; the estimated absolute error from all causes being possibly as large as 17706and the mean absolute deviation 1 3 % for individual measurements, we fol(1) Supported in part by grants from the National Science Foundation, and by NSF and University of Illinois predoctoral fellowships held by F. A. B. (2) Alfred P. Sloan Research Fellow. (3) A. G. Whittaker and D. &I.Yost, J . Chem. Phys.. 17, 188 (1949). (4) F. A. Blankenship and R. L. Belford, zbid., 86, 633 (1962). ( 5 ) F. A. Blankenship, Doctoral Thesis, University of Illinois, June, 1962. (6) E. L. Crubb, F. A. Blankenship, and R. L. Belford, Group on Binding and Structure of Metal Complexes Research Report No. 14, Department of Chemistry, University of Illinois.
